Design and Evaluation of a 3D Road Geometry Based Heavy Truck Fuel Optimization System

Abstract

This dissertation develops a 3D road geometry based optimal powertrain control system in reducing the fuel consumption of heavy trucks. The real-time optimal control (OC) system, solving a constrained nonlinear programming problem, is designed to predict and command the optimal throttle, brake torque (generated from the engine retarder), gear shifting, and velocity trajectory to minimize the fuel consumption and travel time. Throttle and gear shifting are continuous and discrete control inputs respectively, which is a mixeddiscrete nonlinear programming problem (MDNLP). The optimization solver developed is an interior-point algorithm plus a rounding-off method, where all discrete gear ratios are handled as continuous variables and optimized, and then the optimal discrete gear ratios are obtained by rounding up each continuous gear ratio to the nearest discrete value. Simulation and experimental tests of a Class 8 truck are conducted with GIS 3D road geometries. Test results show that the optimal control system is able to reduce fuel consumption up to 3.0% with small travel time increases on level and rolling terrains when compared to the defined baseline. When on the highly mountainous terrain with steep crest slope and long slope length, the OC could only save a small amount of fuel. Thus, it is found that the gain in fuel economy is directly effected by the change in terrain type. Additionally, sensitivity analyses for the terrain and road geometry are conducted to investigate how the change of the terrain and the errors in the terrain data effect the gain in fuel economy and the system performance. For the terrain sensitivity, it is found that the gain in fuel economy is directly related to the change of road grade (both the magnitude and frequency) and slope length. For the terrain error sensitivity, the road error largely effects both the fuel economy and the system performance. This research reveals that the impact from the absolute error (a shift in the slope position) on the fuel savings is not as evident as that from the relative error (a different slope value). The impact from both absolute and relative errors on the system performance is significant, which shows the requirement to apply a high accuracy road map in real road tests as well as in production uses.